The present invention relates to antenna systems for satellite radio communications, and more particularly, to a passive coupling device for a satellite radio antenna system.
Until relatively recently, satellite-based communication systems were used mainly for the transmission of telephone conversations and television broadcasts. Now satellite-based communication systems are being used to transmit radio broadcasts. In particular, the radio industry has recognized that satellite transmission of radio broadcasts allows listeners in cars, trucks, boats, and other vehicles to receive desired radio programming beyond the relatively limited geographic range associated with standard AM and FM radio broadcasting. Thus, for example, using satellite systems a listener can listen to the same radio station across an area of thousands of miles. An example of one currently available satellite radio broadcast service is the Satellite Digital Audio Radio Service (xe2x80x9cSDARSxe2x80x9d).
In order to receive satellite broadcasts, vehicles must be equipped with proper antennas and receivers. Since most vehicles are not yet built with such antennas and receivers as standard equipment, satellite-capable antennas and receivers must be retrofitted on and in the vehicles. Mounting appropriate antennas on existing vehicles presents a particular challenge since it is preferred that the antenna be mounted on the exterior of the vehicle and the receiver be mounted in the interior of the vehicle. Of course, it is also preferred that a wired connection be made between the antenna and receiver.
In many retrofitting applications, glass-mounted antennas are used because of their easy installation. Installing a glass-mounted antenna does not require drilling holes in an exterior vehicle surface in order to mount the antenna and to connect a wire or cable between the antenna and receiver. Thus, a glass-mounted antenna avoids air and water leakage problems, and allows the antenna to be removed from the vehicle without sealing or repairing holes. Although temporarily installed magnet-mounted antennas are available, they are visually obtrusive and require the cable to be passed through an existing door or window opening. As a result, the cables are often damaged.
While glass-mounted radio frequency (xe2x80x9cRFxe2x80x9d) coupling devices avoid the problems of conventional antennas, they introduce different concerns. Current glass-mounted RF coupling devices used in terrestrial cellular communication (which operate in the 800 and 1900 MHz frequency range) exhibit insertion loss characteristics of about 1xc2xd to 2 dB. When these devices are used in a satellite radio transmission system (particularly those that operate above 1 GHz), the loss characteristics increase to an unacceptable level. Loss characteristics are not acceptable due to an increase in the system noise figure (xe2x80x9cNFxe2x80x9d) from the coupler.
Some glass-mounted RF coupling devices compensate for their loss characteristics by using an externally-mounted, low-noise amplifier (xe2x80x9cLNAxe2x80x9d) or other electronics to boost the received signal. While this arrangement may produce more acceptable characteristics, the externally mounted electronics are subjected to environmental hazards and possible tampering. An externally mounted LNA also requires an externally mounted power source or some sort of additional circuitry capable of powering the LNA. An additional DC coupler device can be employed, but this device still requires additional active electronic circuitry and a secondary connection to the power source.
Accordingly, the invention provides a satellite radio antenna with improved loss characteristics. In one embodiment, the invention provides a passive glass-mounted coupler capable of efficiently coupling RF energy through a dielectric panel, without the aid of additional electronic circuits for power. The coupler includes an externally mounted antenna connected to the external unit of the glass-mounted coupler. The internal unit of the glass-mounted coupler mounts on the interior glass surface, juxtaposed with the external unit mounted on the external glass surface. The output of the glass-mounted coupler feeds into the input of a low-noise amplifier (xe2x80x9cLNAxe2x80x9d), which is contained within the housing of the interior unit. The output of the LNA is connected to a coaxial cable, which feeds into the input of a radio receiver. The radio receiver sends a DC signal through the coaxial cable to power the LNA.
In another embodiment, the invention provides an antenna system operable to receive satellite-transmitted signals and terrestrial-transmitted signals, and effectively couple the RF energy of both signals through a dielectric panel (such as a glass panel) using two passive glass-mounted couplers. Each coupler includes an internal unit, mounted on the interior glass surface, juxtaposed with an external unit mounted on the external glass surface. The output of each coupler feeds into one of two LNAs, which is located in the interior housing that encases the internal units.
In another embodiment, the invention provides a radio frequency coupler operable to efficiently couple signals from one side of a dielectric panel to another side. The coupler includes two substantially identical conductive plates, each having an opening of finite dimensions and configuration, and each having a feed point. A first conductor of a first two-conductor transmission line is connected to the first conductive plate, while a second conductor of the first two-conductor transmission line is connected to a first isolated conductive member that extends into the first opening of the first plate. A first conductor of a second two-conductor transmission line is connected to the second plate, while a second conductor of the second transmission line is connected to a second isolated conductive member that extends into the second opening of the second plate. The conductive plates are placed in juxtaposition on opposite sides of the dielectric panel with the isolated conductive members oriented in opposition.
In another embodiment, the invention provides an antenna system that efficiently couples an external radio frequency signal through a dielectric panel to an internal radio frequency amplifying device. The system includes a first conductive plate having an opening of finite dimensions. A first conductive member extends into the opening and is coupled to an external antenna by the center conductor of a transmission line. A shield of the transmission line is coupled to the first conductive plate. The system also includes a second conductive plate having an opening of finite dimensions. A second conductive member extends into the opening and is coupled to a radio frequency amplifying device by the center conductor of another transmission line. A shield of the other transmission line is coupled to the second conductive plate. Both conductive plates are placed in juxtaposition on opposite sides of a dielectric panel with the conductive members oriented in opposition.
In another embodiment, the invention provides a method of coupling radio frequency energy through a dielectric panel having a first surface and a second surface. The method includes the steps of positioning a first radio frequency coupling module on the first surface of the dielectric panel such that a conductive member contacts the dielectric panel. The method also includes the step of creating a radio frequency cavity at least partially around the conductive member to reduce signal leakage. The method also includes positioning a second radio frequency coupling module on the second surface of the dielectric panel such that another conductive member contacts the dielectric panel and is juxtaposed with the first conductive member, with the probes of the modules is opposition. The method also includes the step of creating another radio frequency cavity at least partially around the second conductive member.
As is apparent from the above, it is an advantage of the invention to provide a method and system of coupling radio signals through a dielectric exhibiting relatively low insertion losses. Other features and advantages of the invention will become apparent by consideration of the detailed description and accompanying drawings.